Main brake lights not working/third brake light ok

If your rear brake lights are working, the fuse is good. Check the wiring.

From That Light There Is Only 2 Wires , Trace Them Back To The Tail Light Connection - Most Likely A Split Wire Or Bad Connectio

i had the same problem with a 99 acura cl turns out the rear drivers side tail light was removed and there was a plug on the housing that didnt get plugged in prior

If your third brake light is working then the fuse, and brake switch are ok (it powers up all brake lights). The most likely cause is the column mounted multi-function switch, it consists of the turn signal, hazard and brake light controls, on the right side of steering wheel. You can check at the base of the column. There is a large black three-piece connector there that all the ignition, starter, lights, horn, cruise control and wipers all go thru. With the brake pedal depressed there should be power on the white wire (its on one of the end connectors terminal 1, very first wire, and should have pink wire directly beside it). If power is good, then check for power on the opposite side connector dark green wire terminal 6, and yellow wire terminal 7 (there are near the center directly beside each other). If no power on either (green or yellow) then the multi-function switch is at fault. If power is present on both, then the rear signals must also be out, and you'll have an open connector going to the rear lights.

Your brake peddle switch may be out of adjustment or defective. Look under the dash to the peddle & about half way up you will see the switch. Make sure it is releasing & working properly. Good luck!

checked all fuses even under hood? may have bad signal switch or bad brake light switch yes even if 3rd brake works.also check wiring under rear fender by bumper thats were wire harness is hope this helps.

LH/RH lights cable could be disconnected anywhere, will take a long time to trace.
Center Brake Light and LH & RH should be connected at one point.
Jump a cable from Center Brake Light to one of Rear Break Light.
Hope this will works.

I assume the stop lamp bulbs are OK.
Check the ground connection is ok at the rear brakelamp sockets.

relay

Most likely a short in your break line. You might also check the brake switch, but I would think if the break switch was going, it you wouldn't even have the third lite working...